1. Field of the Invention
The field of the present invention relates to a multi-layered roof module for motor vehicles.
2. Background
EP-A-995 667 and EP-A-1 077 225 describe the preparation of automobile exterior components, such as roof modules, engine hoods etc., wherein deep-drawn colorized thermoplastic sheets or metal foils are reinforced by glass-fiber reinforced polyurethane (PUR). DE-A-100 57 365 describes the preparation of fiber-reinforced plastic sandwich components having an intermediate layer structure.
The deep-drawn sheets usually do not run exactly according to the contour of the mold. This produces an air cushion between the sheet and mold. When a full-surface glass fiber (GF) PUR is introduced, the entrapped air cannot escape from between the sheet and mold during the PUR foaming. The thus entrapped air is partially compressed; the foaming pressure is lower than the pressure of the air between the sheet and mold, resulting in a bulging of the sheet towards the GF PUR. This indentation remains visible on the sheet surface after the molded part has been demolded.
The deep-drawn sheets from thermoplast, aluminum coil coasting or steel coil coating may also be reinforced by another process. In this method, the sheets are inserted in the foaming mold and covered by a layer of GF PUR in a long fiber injection (LFI) PUR method. A honeycomb cardboard is inserted in the reaction mixture while it is still wet. (The honeycomb cardboard may be coated with a glass-fiber mat on both sides thereof. The honeycomb cardboard serves the function of a spacer in the component. This results in a weight reduction as compared to the conventional LFI PUR method.) Now, a second layer of GF PUR is inserted onto the honeycomb cardboard by the LFI PUR method. Subsequently, the mold is closed, and the honeycomb cardboard with the LFI PUR is formed into the desired shape.
For example, a honeycomb cardboard having a thickness of 12 mm is compressed to about 7 mm in the middle zone and about 2 mm in the marginal zone. Due to the high degree of compression in the marginal zone, the air present between the sheet and foaming mold becomes entrapped and cannot escape during the foaming process. This produces partial air cushions that result in the formation of indentations in the sheet.
In addition, it is difficult in this method to foam thread inserts or metal sheet inserts with screwing points in a way as to achieve high tearing-out forces.
In this construction, the trimming edge of the built-in component projects into the wet zone of the vehicle. Due to the capillary action and hydrophilicity of the honeycomb cardboard, an undesirable water absorption by the component may occur. The wet honeycomb may be attacked by microbes, and/or the component may freeze and burst open at freezing temperatures (ice bursting), resulting in a delamination of the exterior coating and reinforcement. In the worst case, this may lead to a drastic deterioration of the mechanical properties.
DE 102 44 287 A1 describes a process for the preparation of a composite element composed of i) a sheet and ii) a reinforcing layer containing a polyurethane, comprising the steps of: (A) inserting a sheet (i) in an open mold, B1) introducing polyurethane system components into the mold on top of the sheet (i), B2) introducing a spacer layer into the mold on top of the introduced polyurethane system components, B3) introducing polyurethane system components into the mold on top of the inserted spacer layer, and C) closing the mold and reacting the introduced polyurethane system components to form a polyurethane (ii), and D) optionally trimming projecting sheet, wherein the dimensions of the spacer layer are selected in such a way that the outer edge of the spacer layer within the composite element has a distance of at least from 10 mm to 300 mm, preferably from 15 to 250 mm, more preferably from 25 to 220 mm, more preferably from 40 to 200 mm, from the edge of the resulting composite element. Further, this specification relates to a composite element composed of i) a sheet and ii) a reinforcing layer containing a polyurethane, wherein a spacer layer is embedded in the reinforcing layer, characterized in that the embedded spacer layer has a horizontal distance of at least from 10 mm to 300 mm, preferably from 15 to 250 mm, more preferably from 25 to 220 mm, more preferably from 40 to 200 mm, from the edge of the composite element, and to the use of the composite element for preparing indentation-free vehicle body exterior parts, especially indentation-free roof modules.
“Indentation-free” within the meaning of DE 102 44 287 A1 means that no unevenness, especially no projections or indentations, can be detected in sheet (i) upon visual inspection of the prepared composite element, i.e., the sheet is in a planar arrangement on the reinforcing layer. However, according to the technical teaching disclosed therein, surfaces having a high optical finish (class A) cannot be prepared.
WO 2006/09939 A1 relates to a process for the preparation of fiber-reinforced composite components in which an exterior sheet is bonded to a layer containing fiber-reinforced polyurethane, characterized in that a) an elastic intermediate layer having a modulus of elasticity of from 0.5 MPa to 50 MPa and a thickness of from 0.3 mm to 6 mm is first applied to the outer sheet having a thickness within a range of from 0.2 mm to 5 mm; and subsequently b) at least one other layer is applied to the back side of the intermediate layer, wherein at least one layer containing fiber-reinforced polyurethane is applied.